Lung cancer is the leading cause of cancer-related death in the world. Despite some advances in early detection and recent improvements in its treatment, the prognosis of the patients with lung cancer remains poor (Parkin et al, Lancet Oncol. 2001 September; 2(9):533-43). On the other hand, esophageal squamous-cell carcinoma (ESCC) is one of the most lethal malignant tumors in the gastrointestinal carcinoma family. The majority of esophageal cancers are advanced at the time of presentation and diagnosis, rendering cure unlikely, especially by surgery alone (Shimada et al., Surgery. 2003; 133(5):486-94). In spite of the use of modern surgical techniques combined with multi-treatment modalities, such as radiotherapy and chemotherapy, the over all 5-year survival rate remains 40-60% (Tamoto et al., Clin Cancer Res. 2004; 10(11):3629-38) while that of lung cancer is only 15% (Parkin et al, Lancet Oncol. 2001 September; 2(9):533-43). In fact, it is reported that recurrent ESCC had developed in almost half of the patients who underwent an apparently curative resection, at a median follow up of 37.3 months (Mariette et al., Cancer. 2003; 97(7):1616-23). Consequently, much research effort has been directed towards studies of adjuvant chemotherapy and chemoradiation, particularly in defining the best regimens from the standpoint of efficacy and minimal toxicity and in an attempt to predict response. However, developments in neoadjuvant and adjuvant therapies have led to mixed conclusions. Collectively, past studies have not shown an optimal neoadjuvant or adjuvant regimen in terms of survival benefit. Therefore, there is an urgent need for novel diagnostic tools for early detection of cancer and molecular-targeted therapies involving small-molecule and antibody-based approaches.
In that vein, several tumor markers are used for diagnosis and follow-up of patients with ESCC, for example, SCC (squamous-cell carcinoma antigen), CEA (carcinoembryonic antigen), and CYFRA 21-1. Recently, serum MK (midkine), CD 147, MMP-2 (matrix metalloproteinase-2), MMP-26 and MMP-9 in patients with ESCC was reported to be associated with poor prognosis (Shimada et al., Cancer Sci. 2003; 94(7):628-32; Kawaguchi et al., Cancer. 2000; 89(7):1413-7; Ishibashi et al., Cancer. 2004; 101(9):1994-2000; Yamamoto et al., Carcinogenesis. 2004; 25(12):2353-60). However, at present, no specific tumor marker is clinically useful for detection of ESCC at an early and potentially curative stage. Therefore, new diagnostic and therapeutic strategies such as development of molecular-targeted agents and antibodies as well as cancer vaccines, are urgently needed. Several tumor markers, such as proGPP, NSE, cytokeratin 19-fragment (CYFRA 21-1), squamous-cell carcinoma antigen (SCC), and carcinoembryonic antigen (CEA) have been increased in the circulation of lung cancer patients (Castaldo G, et al., J Clin Oncol. 1997 November; 15(11):3388-93; Peck et al., Cancer Res. 1998 Jul. 1; 58(13):2761-5; Salerno et al., Chest. 1998 June; 113(6):1526-32.), while SCC, CEA, and CYFRA 21-1 for ESCC, are used in clinic for diagnosis as well as in follow-up of the patients (Shimada et al., Surgery. 2003 May; 133(5):486-94, Kawaguchi et al., Cancer. 2000 Oct. 1; 89(7):1413-7). In NSCLC patients, the sensitivity of CEA was 25% in squamous-cell carcinoma and 50% in adenocarcinoma, whereas, the sensitivity of SCC was 30% in squamous-cell carcinoma (Rastel et al., Eur J. Cancer. 1994; 30A(5):601-6). The sensitivity of CYFRA 21-1 was 57% in squamous-cell carcinoma and 27% in adenocarcinoma (Rastel et al., Eur J. Cancer. 1994; 30A(5):601-6). Reportedly, the positive rate of serum SCC in patients with ESCC was 18% in stage I, 22% in stage II, 34% in stage III, and 37% in stage IV. The incidence of CEA positivity in patients with stage IV ESCC was only 16%. Although CEA was not a prognostic factor, SCC was shown to be an independent prognostic factor to pTNM factors by using multivariate analysis (Shimada et al., Surgery. 2003 May; 133(5):486-94). These facts indicate that no tumor marker has been proven to be useful for detection of lung cancer and ESCC at potentially curative stage, and a limited number of practical prognostic marker is presently available for selection of treatment modalities for individual patients.
Analysis of gene-expression profiles on cDNA microarray enables the comprehensive analysis of gene expression profiles in cancer cells, and some studies describing such transcription profiles have been reported. For example, with regard to ESCC, several studies reported gene expression profiles of human ESCC that are candidates as diagnostic markers or therapeutic targets (Luo et al., Oncogene. 2004; 23(6):1291-9; Kihara et al., Cancer Res. 2001; 61(17):6474-9; Tamoto et al., Clin Cancer Res. 2004; 10(11):3629-38). However, all of the previous studies in human ESCC involved bulk tumor tissues and, since ESCC contains various types of cells, such as mesenchymal cells and inflammatory cells, fail to reflect accurate expressional changes during esophageal carcinogenesis (Nishida et al., Cancer Res. 2005; 65(2):401-9). Accordingly, more accurate studies are needed.
The present invention addresses these needs. Specifically, in an effort to understand the carcinogenic mechanisms associated with cancer and identify targets for developing novel anti-cancer agents, the present inventors performed large scale, genome-wide analyses of gene expression profiles found in purified populations of esophageal cancer cells, including 19 ESCC samples purified by laser microbeam microdissection (LMM), using a cDNA microarray consisting of 32,256 transcribed genes.
To isolate potential molecular targets for diagnosis, treatment, and/or prevention of lung and esophageal carcinomas, the present inventors performed a genome-wide analysis of gene expression profiles of cancer cells from 101 lung cancer and 19 ESCC patients, all of which had been purified by laser microbeam microdissection (LMM) using a cDNA microarray (Kikuchi et al., Oncogene. 2003 Apr. 10; 22(14):2192-205, Int J. Oncol. 2006 April; 28(4):799-805; Kakiuchi et al., Mol Cancer Res. 2003 May; 1(7):485-99, Hum Mol. Genet. 2004 Dec. 15; 13(24):3029-43. Epub 2004 Oct. 20; Yamabuki T, et al, Int J. Oncol. 2006 June; 28(6):1375-84). To verify the biological and clinicopathological significance of the respective gene products, the present inventors have established a screening system by a combination of the tumor-tissue microarray analysis of clinical lung-cancer materials with RNA interference (RNAi) technique (Suzuki et al., Cancer Res. 2003 Nov. 1; 63(21):7038-41, Cancer Res. 2005 Dec. 15; 65(24):11314-25; Ishikawa et al., Clin Cancer Res. 2004 Dec. 15; 10(24):8363-70, Cancer Res. 2005 Oct. 15; 65(20):9176-84; Kato et al., Cancer Res. 2005 Jul. 1; 65(13):5638-46; Furukawa et al., Cancer Res. 2005 Aug. 15; 65(16):7102-10). In the process, the present inventors identified Dikkopf-1 (DKK1) as a novel serological and histochemical biomarker and as a therapeutic target for lung and esophageal cancers.
DKK1 is reported to be a secreted protein which plays a crucial role in head formation in vertebrate development, and is known as a negative regulator of Wnt signaling (Niida et al., Oncogene. 2004 Nov. 4; 23(52):8520-6). Dkk1 binds to LRP5/6 and Kremen proteins, thus inducing LRP endocytosis which prevents the formation of Wnt-Frizzled-LRP5/6 receptor complexes (Gonzalez et al., Oncogene. 2005 Feb. 3; 24(6):1098-103). In spite of these biological studies, there has been no report describing the significance of activation of DKK1 in human cancer and its potential as a diagnostic and therapeutic target.
The present inventors report here the identification of DKK1 as a novel diagnostic and prognostic biomarker and a potential target for therapeutic agents/antibodies, and also provide evidence for its possible role in human pulmonary and esophageal carcinogenesis.